1. Field of the Invention
The field of art to which this invention pertains includes fluid pressure operated mechanisms and more specifically multiple disc wet brakes and clutches.
2. Description of the Prior Art
Multiple disc wet brakes and clutches utilize disc packs located in the fluid retaining cavity of a housing that include a plurality of axially movable or compressible stator discs and a plurality of axially movable or compressible rotor discs, intermediate adjacent ones of the stator discs mounted for rotation with a hub portion. These mechanisms are generally hydraulically actuated via a piston that is hydraulically pressurized. The friction developed between the interfacing surfaces of the stator discs and rotor discs restrains the rotation of the hub in a manner well known in the art.
Two methods of retaining the stator discs in an anchored position are common in the prior art. In one method, as shown in U.S. Pat. No. 3,730,301 to Heck et al, the stator discs are held against rotation in a spline-like manner by fitting about bolts circumferentially spaced about the housing. The second method, as exemplified in U.S. Pat. No. 2,519,965 to Wellman, is to provide the stator discs with a plurality of radially outwardly extending projections and associated grooves, both of a polygonal configuration with sufficient clearance between the tabs and grooves to allow axial movement of the stator discs to provide selective compression of the disc pack. In the first method the bolts are a source of fluid leakage and require special sealing while the polygonally configured projections and depressions of the second method are expensive and time consuming to manufacture.
An additional persistent problem in the prior art wet disc brakes and clutches has been to eliminate or control foreign matter, such as dirt or grease which remained in the brake or clutch housing cavity after original manufacture or repairs, as well as foreign material entering the housing cavity through fluid seals from causing excessive wear on the friction surfaces of the disc pack.